1. Field of the Invention
This invention relates to a method for minimizing deposits when firing tire derived fuels, such as, for example, tire chips, in combination with other fuels. More specifically, the invention relates to a method for minimizing deposits by increasing the level of magnesium in the fuel(s) being burned.
A variety of fuels are used in firing systems such as, for example, large industrial and institutional boilers, furnaces, incinerators, etc. Examples of these fuels include, but are not limited to, residual fuel oils such as No. 6 fuel oil, coal, wood chips, bark, municipal mill sludge, hog fuel, pelletized sawdust, and tire derived fuels such as tire chips. Typically, more than one of these fuels is burned at the same time. Deposits resulting from combustion of these various types of fuel, referred to as fireside deposits, for example ash and slag, are the result of inorganic contaminants or other impurities in the fuel. In the high temperature zone of a typical boiler system, for example the waterwalls, screen tubes, superheaters and convection risers, where temperatures typically reach greater than 1200.degree. F., such fireside deposits ultimately result in an unacceptable lowering of heat transfer efficiency and reduction of boiler service life. In addition, these deposits are an expensive problem in boilers and other systems causing delays and shutdowns for cleaning and removal.
Tire derived fuels are attractive economically, but the concentration of zinc in the fuels is higher than that of almost all other fuels. Zinc not only forms a part of the ash and slag of the fireside deposits, but the reaction of zinc with potassium and sulfur oxides to produce potassium zinc sulfate, among other things, significantly contributes to both the amount of deposit and the rate of build-up. Accordingly, systems burning tire derived fuels will be forced to shutdown more frequently for removal of these excessive deposits than will those systems operating without tire derived fuels.
2. Brief Description of Background Art
U.S. Pat. No. 2,845,338 discloses the use of blends of magnesium oxide and copperoxychloride to inhibit deposit in coal-fired boiler furnaces.
U.S. Pat. No. 4,503,019 discloses the use of blends of magnesium oxide and copperoxychloride to inhibit calcium oxide deposit in coal-fired lime kilns.
U.S. Pat. No. 4,202,671, which is hereby incorporated by reference, discloses an organic magnesium and organic manganese compound for use in reducing fuel oil requirements and sulfur trioxide emissions produced during combustion, but does not disclose use of this compound when firing tire derived fuels.
U.S. Pat. No. 4,512,774 discloses the use of residual fuel oil conditioners in improving combustion deposits and corrosion resulting from the burning of residual fuel oils.
There is no suggestion that the methods and/or compounds disclosed in any of the above references minimize deposits in boilers and furnaces firing a combination fuel including tire derived fuels. Further, use of conventional treatments such as those disclosed in the background art do not produce acceptable results when tire derived fuels are burned. Accordingly, there is a need for a method of minimizing deposits in systems burning tire derived fuels.